It has previously been proposed to position a diamond drawing die, that is, an essentially circular diamond pellet with a hole therethrough to draw wire through the hole on a steel support which is essentially pot-shaped. In cross section, the steel support has an essentially U shape. The diamond itself is secured in position in the steel support by a body of sintered material. The diamond is seated on the flat bottom wall of the pot-shaped steel support, centered and with its bore in alignment with a bore through the steel holder. The sintered body surrounds the diamond; the sintered material is usually a copper-nickel composition. The wire is introduced from the side of the sintered body, that is, from the open side of the pot-shaped holder, through the hole of the diamond, and drawn out from the other end, so that the wire drawing pull force which is exerted by the wire on the drawing die will be accepted directly by the steel support.
In operation, heat arising during drawing can be carried away and dissipated from the diamond directly on the steel support.
The diamond is hard and very brittle; it thus reacts to impacts or shocks by forming fissures, or by shattering. To have long life, it is thus necessary that the diamond drawing die be securely attached to its holder permitting no relative movement and, preferably, irremovably secured in the holder. The diamond itself must be suitably supported with respect to the pulling force exerted by the drawing apparatus. Preferably, it should be under essentially uniform stress with respect to all directions of application of force. It is particularly important to provide for good uniform support in axial and radial direction, with respect to the drawing opening. Any heat which arises should be carried away to the surrounding structure as quickly as possible.
The drawing die as described, that is, the diamond and its support combination, is subject to improvement. It is difficult to reliably attach the diamond to its support. There is little prestressing of the diamond and uneven support of the diamond to accept the drawing forces is difficult to avoid. It is particularly difficult to provide sufficient prestressing since friction occurs upon sintering of the sintering material with respect to the support element. The shape of the support element and of the diamond itself leads to heat transfer difficulty with respect to the socket or holder in which the diamond and its support is to be inserted. It would be desirable to have intimate contact between the sinter body, rather than between the steel support, and the holder for improved heat transfer. The intermediate wall portions of the cup-shaped support in which the diamond is located interferes with effective heat transfer.